Noncorrosive organic derivatives of cellulose



Patented Jan. 18, 1938 UNETED STATES PATENT OFFICE NONCORROSIVE ORGANIC DERIVATIVES OF CELLULOSE Herbert E. Martin and Dorsey A. Ensor, Cumberland, Md, assignors to Celanese Corporation of America, a corporation'of Delaware 9 Claims.

This invention relates to the treatment of organic derivatives of cellulose, such as the organic esters of cellulose, to remove therefrom, or to make inactive, corrosive compounds or compounds that cause the organic derivatives of cellulose to have a corrosive effect on metallic surfaces. The treated organic derivatives of cellulose may be formed into filaments, films and molded .articles without appreciably corroding the spinning jets or other metallic surfaces contacted by solutions .of the organic derivative of. cellulose.

An object .of the invention is the economic and expeditious production of organic derivatives of cellulose that, when .dissolved in a solvent, form solutions that are less corrosive than similar solutions formed of untreated organic derivatives of cellulose. Other objects of the invention will appear from the following detailed description.

In the productionof organic derivatives of cellulose there are produced various compounds that are either corrosive to metals or, when an organic derivative of cellulose is dissolved in a solvent therefor, cause the formation of compounds that are corrosive to metals. Examples of one type of such compounds are those containing sulphur. These compounds, prior to this invention, were separated from the derivatives of cellulose, if at all, only by elaborate and involved treatments. By employing this invention, however, organic esters of cellulose either before, during, or after being stabilized, are treated with an agent that tends toremove corrosive compounds, or compounds which tend to produce corrosive compounds. The treatment with the agent is simple and inexpensive The treatment in accordancewith this invention is carried out to such an extent as to produce an organic derivative of cellulose that .is substantially non-corrosive and is completed in a short period of time.

Organic derivatives of cellulose treated in accordance with this invention may be spun into filaments by extruding the same through jets into a solidifying medium. The organic derivative of cellulose so treated does not attack the metal surrounding the orifice. When the metal of the spinning jet is attacked, the size of the orifice is enlarged or particles of the corroded metal wedged in the orifice, thus producing filaments of undesired denier. Furthermore, since organic derivatives of cellulose treated in accordancewith this invention do not attack metal parts contacted thereby, they do not pick up metallic salts which tend to discolor articles formed therefrom.

In accordance with thisinventionwe treat precipitated or solid organic derivatives of cellulose, preferably, at elevated temperatures, with a dilute solution of a reducing agent, for example stannous chloride, sodium bisulphite and like agents. After this treatment, the derivative of cellulose may be washed substantially free of the treating compound and/or the reaction products formed by same, or, if desired, a trace of the reducing agent may be left in the organic derivative of cellulose. The organic derivative of cellulose may be treated before or after the treatment with the reducing agent with chlorine or chlorine-liberating compounds such as sodium hypochlorite and the like. The organic derivative of cellulose thus treated, when dissolved in a solvent therefor, forms a solution which is substantially non-corrosive.

This invention is especially applicable to the treatment of any organic esters of cellulose such as cellulose acetate, cellulose formate, cellulose propionate and cellulose butyrate made by proc- T ess'esthat tend to produce corrosive materials. It is also applicable, by obvious modifications, to the treatment of nitrocellulose, cellulose ethers and mixed esters and ethers of cellulose. Examples of cellulose ethers are ethyl cellulose, methyl cellulose and benzyl cellulose.

The organic esters of cellulose that lend themselves to this invention may be made by any of the methods now employed to make the same. For example, cellulose (cottondinters, cotton, Wood pulp, etc.) with or without a pretreatment in organic acid such as acetic acid and formic acid, is esterified by treating the same with an acid anhydride in the presence of an acid 501- vent and a catalyst. In place of the acid solvent or in connection therewith there may be used suspension liquids such as benzol. The acid solvent may be a concentrated acid corresponding to the anhydride employed or it may be, as is preferred, glacial acetic acid. Examples of catalysts are sulphuric acid, phosphorous acid, hydrochloric acid, zinc chloride and mixtures of these.

After e sterification, suflicient water may be added to convert any remaining anhydride to the corresponding acid and the mixture hydroly zed 'or ripened until the desireds'olubility characteristics are developed. The catalyst is .then neutralized and water or other nonsolvent ifor the ester added to precipitate theester. During this precipitation step the ester may, if desired, be treated with a solution of a hypochlorite or other chlorine-liberating compound to bleach the same. The ester is thenseparated and washed free of the acid solution. The cellulose ester may then be stabilized by treating with boiling water containing small amounts of mineral acid or with steam with or Without pressure. Although stabilized, the ester may contain compounds which, when the ester is in solution, cause the solution to corrode or attack metals.

We have found that, if the ester is treated after the precipitation, but prior to stabilizing, by soaking the ester in a dilute aqueous solution of a reducing agent, the resulting ester is substantially free of the compounds, the exact chemical structure of which is unknown, that cause the ester or solution thereof to have a corrosive effect on metals. We have also found that these undesirable compounds may be removed or diminished to below an effective quantity by soaking the stabilized ester in a dilute solution of a reducing agent. The latter method of treating stabilized esters is preferable as it is in general more eifective and has less tendency to alter the viscosity and the solubility characteristics of the ester. The soaking treatment is preferably carried on at elevated temperatures, for instance, at from 50 to 100 0. Although soaking the precipitated derivative of cellulose in a dilute solution of a reducing agent is the preferred method of treatment, other methods may be employed such as spraying the solution of the reducing agent on the derivative of cellulose, or working the derivative of cellulose in a counter-current manner in a stream of the dilute solution of the reducing agent. The treating liquid or bath may be formed by dissolving any suitable reducing agent in an aqueous medium. The reducing agentmay be, for example, sodium bisulphite, etc. The amount of the aqueous solution of the reducing agent is preferably from 4 to 20 or more times the weight of the derivative of cellulose. The concentration of the aqueous solution being such that the amount of reducing agent used is between 0.03 to 1% on the Weight of the derivative of cellulose employed, and is preferably from 0.1 to 0.5%. Although the treating bath may be of any suitable temperature, for instance, from 50 to 100 C., it has been found preferable to maintain the temperature at from 80 C. to the boiling point of the bath. Although an elevated temperature is preferred, effective results may be obtained at room temperature by prolonging the length of treatment.

The treatment of the derivative of cellulose with the reducing agent may be preceded or followed by a treatment with an alkaline hypochlorite. The alkaline hypochlorite treatment is not absolutely necessary, however, and the treatment with the reducing agent is sufficient to form non-corrosive derivatives of cellulose where it is undesirable to use thereon chlorine bleaching agents.

To further describe the invention and not as a limitation, the following examples are given:

Example I Precipitated stabilized cellulose acetate, after being washed to a neutral state, is boiled for four hours in an aqueous bath containing from .35 to .4% on the weight of the cellulose acetate of sodium bisulphite. The bath is approximately 20 times the weight of the cellulose acetate. The cellulose acetate is then washed substantially free of the inorganic salts, dried and dissolved in a suitable solvent. The resulting solution is found to be substantially free of any corrosive compounds.

Example If Unstabilized cellulose acetate, after being Washed to neutral state, is boiled for four hours in an aqueous bath containing from .3 to .45% on the weight of the cellulose acetate of sodium bisulphite. The bath is approximately 20 times the Weight of the cellulose acetate. The stabilizing of the cellulose acetate is then carried out in the same bath by the addition of a sufficient quantity of sulphuric acid. The cellulose acetate is then washed substantially free of the inorganic salts, dried and dissolved in a suit-able solvent. The resulting solution is found to be substantially free of any corrosive compounds.

Example [I I Precipitated stabilized cellulose acetate, after being washed to a neutral state, is boiled for four hours in an aqueous bath containing from .05 to .15% of stannous chloride on the weight of the cellulose acetate. The bath is approximately 20 times the weight of the cellulose acetate. The cellulose acetate is then washed substantially free of the inorganic salts, dried and dissolved in a suitable solvent. The resulting solution is found to be substantially free of any corrosive compounds. If desired, a small percent of hydrochloric acid may be added to the bath containing the stannous chloride.

It is to be understood that the foregoing detailed description is given merely by Way of illustration and that many variations may be made therein without departing from the spirit of our invention.

Having described our invention, what We desire to secure by Letters Patent is:

1. Method of reducing the corrosive properties of a derivative of cellulose, which comprises treating the derivative of cellulose in the form precipitated from a solution thereof with a reducing agent, selected from the group consisting of an alkali bisulphite and stannous chloride, in a quantity sufiicient to remove the corrosive compounds without substantially altering the viscosity and solubility characteristics of the derivative of cellulose.

2. Method of reducing the corrosive properties of an organic acid ester of cellulose, Whichcomprises treating the organic acid ester of cellulose in the form precipitated from a solution thereof with a reducing'agent, selected from the group consisting of an alkali bisulphite and stannous chloride, in a quantity sufficient to remove the corrosive compounds without substantially a1- tering the viscosity and solubility characteristics of the organic acid ester of cellulose.

3. Method of reducing the corrosive properties of cellulose acetate, which comprises treating the cellulose acetate in the form precipitated from a solution thereof with a reducing agent, selected from the group consisting of an alkali bisulphite and stannous chloride, in a quantity sufiicient to remove the corrosive compounds without substantially altering the viscosity and solubility characteristics of the cellulose acetate.

4. Method of reducing the corrosive properties of an organic acid ester of cellulose, which comprises treating the organic acid ester of cellulose in the form precipitated from a solution thereof with a dilute aqueous solution of a reducing agent, selected from the group consisting of an alkali bisulphite and stannous chloride, in a quantity sufficient to remove the corrosive compounds without substantially altering the viscosity'and solubility characteristics of the organic acid ester of cellulose.

5. Method of reducing the corrosive properties of cellulose acetate, which comprises treating the cellulose acetate in the form precipitated from a solution thereof with a dilute aqueous solution of a reducing agent, selected from the group consisting of an alkali bisulphite and stannous chloride, in a quantity sufiicient to remove the corrosive compounds without substantially altering the viscosity and solubility characteristics of the cellulose acetate.

6. Method of reducing the corrosive properties of a stabilized organic acid ester of cellulose, which comprises treating the stabilized organic acid ester of cellulose in the form precipitated from a solution thereof with a reducing agent, selected from the group consisting of an alkali bisulphite and stannous chloride, in a quantity sufiicient to remove the corrosive compounds without substantially altering the viscosity and solubility characteristics of the organic acid ester of cellulose.

'7. Method of reducing the corrosive properties of stabilized cellulose acetate, which comprises treating the stabilized cellulose acetate in the form precipitated from a solution thereof with a reducing agent, selected from the group consisting of an alkali bisulphite and stannous chloride, in a quantity sufficient to remove the corrosive compounds without substantially altering the viscosity and solubility characteristics of the cellulose acetate.

8. Method of reducing the corrosive properties of an organic acid ester of cellulose without substantially altering the viscosity and solubility charactertistics thereof, which comprises treating the organic acid ester of cellulose in the form precipitated from a solution thereof with a reducing agent, selected from the group consisting of an alkali bisulphite and stannous chloride, in an amount equal to from 0.03 to 1% based on the weight of the organic acid ester of cellulose present.

9. Method of reducing the corrosive properties of cellulose acetate without substantially altering the viscosity and solubility characteristics thereof, which comprises treating the cellulose acetate in the form precipitated from a solution thereof with a reducing agent, selected from the group consisting of an alkali bisulphite and stannous chloride, in an amount equal to from 0.03 to 1% based on the weight of cellulose acetate present.

HERBERT E. MARTIN. DORSEY A. ENSOR. 

